[PATCH] x86/vtd: relax EPT page table sharing check

[PATCH] x86/vtd: relax EPT page table sharing check

[Roger Pau Monne]

The EPT page tables can be shared with the IOMMU as long as the page
sizes supported by EPT are also supported by the IOMMU.

Current code checks that both the IOMMU and EPT support the same page
sizes, but this is not strictly required, the IOMMU supporting more
page sizes than EPT is fine and shouldn't block page table sharing.

This is likely not a common case (IOMMU supporting more page sizes
than EPT), but should still be fixed for correctness.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Jan Beulich <jbeulich@suse.com>
---
Changes since v1:
 - Use <= to compare caps.
 - Reword subject/commit message.
---
 xen/drivers/passthrough/vtd/iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 07d40b37fe..208b33c0e4 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1914,8 +1914,8 @@ static int __init vtd_ept_page_compatible(struct vtd_iommu *iommu)
     if ( rdmsr_safe(MSR_IA32_VMX_EPT_VPID_CAP, ept_cap) != 0 ) 
         return 0;
 
-    return (ept_has_2mb(ept_cap) && opt_hap_2mb) == cap_sps_2mb(vtd_cap) &&
-           (ept_has_1gb(ept_cap) && opt_hap_1gb) == cap_sps_1gb(vtd_cap);
+    return (ept_has_2mb(ept_cap) && opt_hap_2mb) <= cap_sps_2mb(vtd_cap) &&
+           (ept_has_1gb(ept_cap) && opt_hap_1gb) <= cap_sps_1gb(vtd_cap);
 }
 
 /*
-- 
2.26.0

Re: [PATCH] x86/vtd: relax EPT page table sharing check

[Jan Beulich]

On 17.04.2020 13:29, Roger Pau Monne wrote:
> The EPT page tables can be shared with the IOMMU as long as the page
> sizes supported by EPT are also supported by the IOMMU.
> 
> Current code checks that both the IOMMU and EPT support the same page
> sizes, but this is not strictly required, the IOMMU supporting more
> page sizes than EPT is fine and shouldn't block page table sharing.
> 
> This is likely not a common case (IOMMU supporting more page sizes
> than EPT), but should still be fixed for correctness.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

RE: [PATCH] x86/vtd: relax EPT page table sharing check

[Tian, Kevin]

> From: Roger Pau Monne <roger.pau@citrix.com>
> Sent: Friday, April 17, 2020 7:30 PM
> 
> The EPT page tables can be shared with the IOMMU as long as the page
> sizes supported by EPT are also supported by the IOMMU.
> 
> Current code checks that both the IOMMU and EPT support the same page
> sizes, but this is not strictly required, the IOMMU supporting more
> page sizes than EPT is fine and shouldn't block page table sharing.
> 
> This is likely not a common case (IOMMU supporting more page sizes
> than EPT), but should still be fixed for correctness.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>